v0.2.0 is released, Support Promise now

• add askForPermission phase in Lifecyle. which is useful for control navigation.
• support Promise in enter， leave and canEnter, canLeave( introduced in v0.2.0) to help us implement some asynchronous navigation. #7
• add namespace support for builtin emitter #16
• remove [state.async], you can use option.async for asynchronous navigation. but I suggest you to use promise instead. The only change that isn't backward-compatible.
• remove $notfound #11
• coverage is almost 100% now .
• take watch as the default task #13
• unify the routing option.